Method and device for controlling an internal combustion engine

ABSTRACT

A method and a device for controlling an internal combustion engine having a central control unit and a peripheral control unit are described. The central control unit transmits request signals to the peripheral control unit. At least two load circuits receive control signals from the peripheral control unit. The peripheral control unit checks the request signals and/or additional signals for plausibility.

BACKGROUND INFORMATION

[0001] The present invention is directed to a method and a device forcontrolling an internal combustion engine.

[0002] A central control unit and a peripheral control unit are providedfor the control, the central control unit transmitting request signalsto the peripheral control unit. Based on these request signals, theperipheral control unit transmits control signals to load circuits.These load circuits are, in particular, injectors controlling themetering of fuel into the internal combustion engine.

[0003] It is especially advantageous in this context that the peripheralcontrol unit checks the request signals and/or further signals forplausibility, thereby substantially increasing the control reliability.It is also advantageous that the central control unit only suppliessimply formed request signals, which merely define the beginning and endof the injection. The peripheral control unit then converts thesesignals into certain current and voltage profiles required forcontrolling the injectors. Moreover, the peripheral control unit mayimplement a monitoring of the injectors and output stages. Furthermore,an individual adaptation to the injectors is possible when using aperipheral control unit. On the other hand, the central control unit maybe used in a global manner for different injectors. This results inconsiderable cost savings since the central control unit may bemanufactured in large quantities due to the fact that the adaptation tothe various injectors occurs in the peripheral control unit.

[0004] From DE 198 21 561, a method of a device for monitoringelectromagnetic load circuits is known. In this case, the voltage and/orthe current flowing through a booster capacitor or present at thebooster capacitor, are/is monitored for plausibility.

[0005] Furthermore, a method and a device for controlling at least oneload circuit are known from the German Patent 195 39 071. In that case,the load circuits are divided into at least two groups, the costly andcomplex components in each case only being provided for one group.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention is explained in the following in terms ofthe specific embodiments shown in the drawing.

[0007] The figures show:

[0008]FIG. 1 a block diagram of the device according to the presentinvention;

[0009]FIG. 2a block diagram of the peripheral control unit;

[0010]FIG. 3 various signals plotted over time; and

[0011]FIG. 4 a flow chart to illustrate the procedure according to thepresent invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0012] The present invention is preferably used in internal combustionengines, especially in internal combustion engines having self-ignition.The metering of fuel there is controlled by injectors, which areactuated with the aid of electromagnetic valves or by piezo-actuators.In the following, these injectors, or these valves or actuators, arereferred to as load circuits.

[0013]FIG. 1 shows the essential elements of the device according to thepresent invention. A central control unit is denoted by referencenumeral 100. It receives signals from various sensors. These are, firstof all, a first sensor 110, which provides a signal FP regarding thedriver input; a second sensor 120, providing signal NW regarding thecamshaft rotation; and a third sensor 130, which supplies a signal KWregarding the crankshaft position. Used as sensors 120 and/or 130, inparticular, are sensors which sample incremental gears or segmentalwheels. These sensors provide pulses having fixed angular spacing.

[0014] The central control unit transmits various request signals A1through A8 to a peripheral control unit 150. The number of requestsignals preferably corresponds to the number of load circuits to becontrolled. Furthermore, central control unit 100 transmits signal KWregarding the crankshaft position to peripheral control unit 150. Ineach case, request signals A1 through A8 are preferably transmitted viaa line. Moreover, central control unit 100, peripheral control unit 150and additional units (not shown) are connected via a communicationsystem which, in particular, is implemented as a CAN bus.

[0015] Peripheral control unit 150 in turn is connected via lines toload circuits 161 through 168, which are each acted upon with controlsignals S1 through S8. The specific embodiment shown relates to aninternal combustion engine having eight cylinders. However, theprocedure according to the present invention may also be used ininternal combustion engines having a different number of cylinders.

[0016] Peripheral control unit 150 is connected to a supply voltage Ubatvia a switching means 170, which is able to be controlled by centralcontrol unit 100.

[0017] On the basis of the different variables characterizing theoperating state, the ambient conditions and/or the driver input, centralcontrol unit 100 defines request signals Al through A8. These requestsignals determine the beginning, the end and, thus, the duration of themetering of fuel. In appropriately designed load circuits, this signalmay be used for the direct control of a switching means for supplyingcurrent to a load circuit, especially a solenoid valve. A problem ariseswhen load circuits are used which require a particular currentcharacteristic and/or a particular voltage characteristic for precisecontrol.

[0018] Often, fast-switching solenoid valves are used to which anincreased voltage, also known as booster voltage, is supplied at thebeginning. In the further course, the current is limited to a holdingcurrent. This current characteristic is preferably realized by specialoutput-stage components or output-stage circuits. If these output-stageelements are integrated in the central control unit, a different centralcontrol unit has to be manufactured for each injector type. However, ifthe output stage is in a structurally separate location from theinjectors, faults may occur in the data transmission between the centralcontrol unit and the output stage.

[0019] For this reason, the present invention provides a peripheralcontrol unit 150 which converts the general request signals into specialcontrol signals and simultaneously implements a diagnosis, especially ofthe request signals. The diagnosis result is signaled back to centralcontrol unit 100, preferably via the CAN bus. It is particularlyadvantageous that the central control unit, once a fault has beendetected, is able to shut down the peripheral control unit and, thus,the load circuits, by activating switching means 170.

[0020] In addition to monitoring request signals A1 through A8, adiagnosis of the injectors and/or the appropriate wirings of theoutput-stage components is possible as well.

[0021] It is particularly advantageous that the peripheral control unitbrings about a phase, shift of 90°. This means that the control signalsfor a particular cylinder are only triggered upon completion of theplausibility check, that is, when the request signal is available in itsentirety. In this way, it is possible to cut off the control of thecorresponding load circuit and/or of all load circuits in the event of afault.

[0022] A detailed representation of the peripheral control unit is shownin FIG. 2. Elements already described in FIG. 1 are marked withcorresponding reference numerals in FIG. 2. Peripheral control unit 150essentially includes a first monitoring system 210 to which signal KW istransmitted; a second monitoring system 220 to which request signals A1through A8 are transmitted; a control calculation 230; and an outputstage 240 which provides control signals S1 through S8. In oneembodiment it may also be provided that the output stage is in alocation that is structurally separate from peripheral control unit 150.

[0023] Control calculation 230 receives signals from the firstmonitoring system and the second monitoring system and transmits asignal to output stage 240. Output stage 240 sends a signal to secondmonitoring system 220. Furthermore, the first and the second monitoringsystem exchange signals. Second monitoring system 220 acts upon the CANbus with a signal.

[0024] In FIG. 3, different signals are plotted over time. In partialFIG. 3a, different angular ranges of the crankshaft have been marked fora first group of load circuits, and in FIG. 3b permissible requestsignals are shown by way of example. In partial FIG. 3c, differentangular ranges of the crankshaft have been marked for a second group ofload circuits; and in FIG. 3d permissible request signals are shown, byway of example. FIG. 3e shows a partial area of FIG. 3a; and FIG. 3d apartial area of FIG. 3b in an enlarged view.

[0025] In FIG. 3a, angular ranges for a first group of load circuitshave been marked by perpendicular lines. The corresponding requestsignals are shown in partial FIG. 3b. The angular range between point t1and point t3 marks the angular range in which a request signal A1 ispermitted for a first load circuit. The angular range between point t3and point t5 marks the angular range in which a request signal A3 ispermitted for a second load circuit. The angular range between point t5and point t7 marks the angular range in which a request signal A5 isallowed for a third load circuit. The angular range between point t7 andpoint t1 marks the angular range in which a request signal A7 is allowedfor a fourth load circuit. In the example shown, the interval betweentwo respective points defines an angular range of 180° crankshaft angle.In this context, the conditions in an internal combustion engine havingeight cylinders are represented. In an internal combustion engineshaving fewer cylinders, the angular ranges may be selected to becorrespondingly larger.

[0026] Accordingly, the angular ranges and the request signals of asecond group of load circuits are shown in FIGS. 3c and 3 d. In eachcase, load circuits that follow one another in the ignition sequencehave been assigned to different groups of load circuits.

[0027] In FIG. 3, a special embodiment for an internal combustion enginehaving eight cylinders is shown. In this case, the load circuits havebeen divided into two groups, the angular ranges of two cylindersbelonging to the same group immediately adjoining each other. Angularranges of two cylinders belonging to different groups may overlap oneanother. It is also possible to select the angular ranges such that agap remains between the angular ranges of two cylinders belonging to thesame group. This means that there exists an angular range in whichrequest signals are not allowed. The angular ranges may be arbitrarilypredefined, depending on the requirements.

[0028] Essential is that an angular range is specified for every requestsignal. If the request signals impinges upon this angular range, it isrecognized as plausible. In this context, the angular ranges of theindividual request signals may overlap, may be spaced apart, or maytouch.

[0029] In FIGS. 3a through 3 d, the conditions of an internal combustionengine having eight cylinders are shown. In an internal combustionengine having fewer cylinders, the angular ranges are correspondinglysmaller.

[0030] Partial FIGS. 3a through 3 d, show merely a simple embodimenthaving only one partial injection. In additional embodiments, especiallyof internal combustion engines equipped with an exhaust gasaftertreatment system, additional partial injections may be provided.This is illustrated in partial FIGS. 3e and 3 f, which show an enlargedrepresentation of the angular range between t1 and t3 and thecorresponding request signals. In this case, the injection is dividedinto a pre-injection between points t11 and t12 and a main injectionbetween points t13 and t14.

[0031] First monitoring system 210 implements a plausibility check ofrequest signals A1 through A8 using crankshaft signal KW. A fault isdetected when the request signal lies outside of the specific angularranges of the crankshaft. In this case, as shown in FIG. 3, the allowedangular range for the first request signal is defined by instants t1 andt3, for instance. According to the present invention, it is checkedwhether the request signal begins and/or ends in a specific angularrange.

[0032] In an alternative exemplary embodiment, it is also possible toprocess a camshaft signal instead of the crankshaft signal.

[0033] If the specific request signal lies inside this angular range,the request signal is detected as plausible. Given a particular numberof cylinders, these angular ranges may overlap. This is the case, forinstance, in an internal combustion engine having eight cylinders, asshown in FIG. 3.

[0034] Moreover, a proper request signal is only detected if theduration of the fuel injection has a particular length, i.e. when theinterval between instants t13 and t14 is greater than a first thresholdvalue, or if it is smaller than a second threshold value. If the signalis shorter than the threshold value, the request signal is too short, oran interference pulse has to be assumed. If the request signal is toolong, a continuous injection has to be assumed. Corresponding faults aredetected by second monitoring system 220.

[0035] If the first or the second monitoring system detects a relevantfault, this will be transmitted via the CAN-bus to the central controlunit, which then takes appropriate measures. In particular, it initiatesan emergency driving operation or switches off the peripheral controlunit, thereby deactivating the output stages.

[0036] On the basis of request signals A1 and A8 and crankshaft signalKW, control calculator 230 calculates the required current profileand/or voltage profile so as to control the load circuits in anappropriate manner. This signal reaches output stage 240. A device, forinstance, as it is known from the related art, may be used as the outputstage. Preferably an output stage having at least one high-side switchand at least one low-side switch are utilized. A common high-side switchis preferably used for all load circuits or a group of load circuits. Byappropriate control of the high-side switch and the low-side switch, asuitable current/voltage profile is then obtained at the load circuit.

[0037] One operating cycle, i.e., one engine rotation, is made up of twocrankshaft rotations. This means that the peripheral control unit isunable to directly detect in which of the two crankshaft rotations itpresently is. Therefore, the peripheral control unit does not clearlyrecognize, for instance, whether the angular range between t1 and t3 orthe angular range between t5 and t7 is present. A synchronization isrequired for this.

[0038] The synchronization procedure is as follows. In a first step, itis checked whether a permissible request signal is present, all checkspreferably being implemented in the process. If it is detected that therequest signal is in the permissible angular range, synchronization hastaken place. If it is detected that the request signal is outside of thepermissible angular range, it is checked whether the request signal inthe angular range phase-shifted by 360 degrees is plausible. If this isthe case, a new synchronization is implemented. If the request signal inthis angular range is not permissible either, a fault is detected.

[0039] Normally, it is provided that the output stage also monitors forfaults. For instance, it may be provided that the currents flowingthrough the load circuit, and/or the dropping voltage values at the loadcircuit or at components of the output stage are monitored. Especiallyfrom the related art it is known to monitor the voltage at a so-calledbooster capacitor. This booster capacitor supplies the increased voltagerequired in the switching-on process, which generally is higher than thesupply voltage. If the output stage detects a corresponding fault, thisis also reported to the second monitoring system and forwarded fromthere to the central control unit via the CAN-bus.

[0040] This procedure for monitoring and checking the plausibility ofthe signals is represented in FIG. 4 with the aid of a flow chart. Afirst query 400 checks whether two request signals A1 through A8 occursimultaneously. It is checked, in particular, whether the beginningand/or the end of two request signals occur(s) simultaneously or nearlysimultaneously.

[0041] If this is the case, i.e., two request signals are present at thesame time, a query 410 checks whether a special operating state ispresent. In these special operating states, it may happen that fuel ismetered in two cylinders simultaneously. This is the case, for instance,in internal combustion engines having eight cylinders, when apost-injection takes place for exhaust-gas aftertreatment. In such aspecial operating state two simultaneously occurring request signals donot constitute a fault if the two request signals each occur withintheir permissible angular ranges or in their permissible time interval.

[0042] If such a special operating state does not exist, the programconcludes with step 420. In step 420, a fault is detected and acorresponding signal transmitted via the CAN-bus. If two request signalsA1 through A8 occur simultaneously, a short circuit between two linesbetween the central control unit and the peripheral control unit must beassumed.

[0043] In internal combustion engines in which such simultaneousinjections cannot occur, step 410 may be omitted. In this case it isimmediately switched to step 420 and a fault detected when query 400detects simultaneous injections.

[0044] If query 400 detects that none of signals A1 through A8 occur atthe same time, a query 430 checks whether the request signals occur in apermissible angular range, that is, it is checked whether the requestsignals of a specific cylinder are in the appropriate angular range. Forinstance, the request signal for the first cylinder must occur betweeninstant t1 and t3.

[0045] If one of these conditions is not satisfied, i.e., the requestsignal occurs outside of a specific angular range of the crankshaft orthe camshaft and/or outside of a particular time interval, the programends in step 420. If all conditions are satisfied, query 440 follows.

[0046] Query 440 checks whether the duration of the request signal istoo long or too short. If this is the case, i.e., the request signal istoo long or too short, the program ends with step 420. If the requestsignal satisfies the required condition, step 450 follows. This querychecks whether the duration of the injection is plausible. Normally, therequest signal is significantly shorter than a segment.

[0047] In query 450, it is checked whether the interval between tworequest signals satisfies certain criteria. In particular, the intervalbetween two request signals must be greater than a threshold value; ifthis is not the case, the program also ends with step 420. If this isthe case, i.e. the intervals between the request signals are plausible,step 460 follows. Preferably, the interval between two partialinjections is checked for plausibility, that is, it is checked whetherthe interval between instants t12 and t13 assumes a permissible value.

[0048] It is particularly advantageous if the number of partialinjections is counted. For monitoring, this determined number of partialinjections is compared to the number of partial injections transmittedby the central control unit. To this end, it is required that thecentral control unit or the peripheral control unit transmit thecorresponding number via the CAN-bus.

[0049] In step 460 it is checked whether the current values and/orvoltage values measured and/or acquired by the output stage assumeplausible values. If this is not the case, the program also ends withstep 420. If this is the case, a faultfree operation is detected in step470. As an alternative, it may also be provided that output stage 240implements a fault monitoring and transmits a signal to the monitoringsystem in case of a specific fault. In this embodiment, query 460 merelychecks whether a corresponding fault signal is present from output stage240.

[0050] In FIG. 4, the various checks occur in succession over time. Adifferent check sequence may be selected as well. It is particularlyadvantageous if the queries are processed in parallel.

[0051] Especially advantageous is an embodiment in which the check forthe permissible angular range, i.e., query 430, occurs as the lastquery. If query 430 detects that the request signal is not within thepermissible angular range, it is checked whether the request signal inthe angular range, phase-shifted by 360 degrees, is plausible. If thisis the case, a new synchronization is implemented. If the request signalin this angular range is impermissible as well, a fault is detected.

What is claimed is:
 1. A method for controlling an internal combustionengine having a central control unit and a peripheral control unit, thecentral control unit transmitting request signals to the peripheralcontrol unit and at least two load circuits receiving control signalsfrom the peripheral control unit, the peripheral control unit checkingthe request signals and/or additional signals for plausibility.
 2. Themethod as recited in claim 1, wherein a fault is detected when therequest signal occurs outside of a specific angular range of thecrankshaft or the camshaft and/or outside of a specific time interval.3. The method as recited in claim 1 or 2, wherein a fault is detectedwhen a first or a second request signal occurs simultaneously.
 4. Themethod as recited in claim 3, wherein no fault is detected when thefirst and the second request signals occur within a permissible angularrange or a permissible time interval.
 5. The method as recited in one ofthe preceding claims, wherein a fault is detected when the requestsignal is shorter than a first threshold value and/or longer than asecond threshold value.
 6. The method as recited in one of the precedingclaims, wherein a fault is detected when the interval between a firstand a second request signal is smaller than a threshold value.
 7. Themethod as recited in one of the preceding claims, wherein a fault isdetected when the current values and the voltage values in the region ofthe output stage assume implausible values.
 8. A device for controllingan internal combustion engine having a central control unit and aperipheral control unit, the central control unit transmitting requestsignals to the peripheral control unit, and at least two load circuitsreceiving control signals from the peripheral control unit, theperipheral control unit checking the request signals and/or additionalsignals for plausibility.